Determination of Catecholamines in a Small Volume (25 μL) of Plasma from Conscious Mouse Tail Vein

The determination of plasma catecholamine levels is commonly used as a measure of the sympathetic nervous system's response to stress and is highly important for diagnosis, therapy, and prognosis of cardiovascular diseases, catecholamine-secreting tumors arising from the chromaffin cells of the sympathoadrenal system, and affective disorders. Diseases in which catecholamines are significantly elevated include pheochromocytoma, Parkinson's disease, Alzheimer's disease, neuroblastoma, ganglioneuroblastoma, von Hippel-Lindau disease, baroreflex failure, chemodectina (nonchromaffin paraganglioma), and multiple endocrine neoplasia. Plasma norepinephrine levels provide a guide to prognosis in patients with stable, chronic, and congestive heart diseases. The method described here for the determination of plasma catecholamines is based on the principle that plasma catecholamines are selectively adsorbed on acid-washed alumina at pH 8.7 and then eluted at a pH between 1.0 and 2.0. Upon injection, catecholamines in elutes were separated by a reversed phase C-18 column. After separation, the catecholamines present within the mobile phase enter the electrochemical detector. Electrochemical detection occurs because electroactive compounds oxidize at a certain potential and thereby liberate electrons that create measurable current. Catecholamines readily form quinones under these conditions, get oxidized, release two electrons, and create current. The electrochemical detector detects this electrical current that linearly correlates to the catecholamine concentration loaded into the ultra-performance liquid chromatography instrument. A 15-min mixing time during the adsorption and desorption steps was found to be optimal. If the washing step was omitted, the catecholamines could not be eluted from the acid-washed alumina. To prevent dilution, the alumina had to be centrifuged and not aspirated to dryness after the washing step. We report here that by changing the range in the electrochemical detector, plasma catecholamines were measured with only 12.5 μL of plasma and more reliably with 25 μL of plasma. The detection limit was 1 ng/mL. This assay method is very useful as blood can be collected from the tail vein in a conscious mouse and the same mouse can be used for time-dependent or age-dependent studies.